SMAD4 and squamous cell carcinoma: To identify the correlations between miR-301a and SMAD4 in lung cancer of clinical patients from the TCGA (Cancer Genome Atlas) databases, we choose two type of lung cancer, adenocarcinoma (n = 430) and squamous cell carcinoma (n = 332) with normal lung tissue samples to analyze the expression of miR-301a and SMAD4.